Conventional compact discs (CDs) or DVD-ROMs are optical discs employing a pit recording system. An optical pickup is caused to sweep along a track including pits, and the light reflected therefrom is measured to reproduce the information recorded by the pits. Up to now, tracking error signals having the same polarity at all times are produced according to the amount of deviation of the optical pickup from a target track, so that these tracking error signals have directly been used for tracking servo control, referred to below simply as tracking control.
However, when reading out the information from an optical disc, including lands and grooves, such as DVD-RAM, the tracking error signals are inverted in polarity from the case where the read-out destination is a land to the case where the read-out destination is a groove, and vice versa, so that the tracking error signals cannot directly be used for tracking control.
In reproducing the information from an optical disc, as discussed above, “track jump” for continuously accessing the information recorded on a physically separated track is realized, with the minimum unit in the track jump operation being the transition from a given pit to an adjacent pit of the optical pickup. Meanwhile, in this jump operation, the track jump operation is completed by one period of the tracking error signals.
On the other hand, when reading out the information from an optical disc including lands and grooves, such as DVD-RAM, it may incidentally be necessary to perform a “half-track-jump operation” of continuously accessing different structural portions, such as accessing a land and a groove in this order or accessing a groove and a land in this order.
However, in such case, it is necessary to complete the half-track jump operation within one half period of the tracking error signal obtained during the track jump operation, such that there is raised a problem that a conventional control method of completing the track jump by one period of the tracking error signal cannot be directly applied.
Moreover, in an optical pickup, the distance thereof from an optical disc is controlled, according to focusing-error signals, for realizing optimum information reproduction. These focusing-error signals are corrected according to a focusing bias value, referred to below simply as a bias value, and are controlled so as to minimize the jitter of the produced RF signals.
However, in reading out the information from an optical disc including lands and grooves, such as DVD-RAM, an optimum bias value for the case where the read-out destination is the land differs from those for the case where the read-out destination is the groove, so that there is raised a problem that, if the focusing-error signals are corrected from a sole bias value, as conventionally, optimum RF signals cannot be obtained from the land and the groove.
Meanwhile, the reason why the optimum bias value for the case where the readout destination is the land differs from that for the case where the readout destination is the groove is that the distance from the optical pick-up to the land differs from that from the optical pickup to the groove.